Coupons, where is stored the quota per user?

Hi,

That's normal. That information is not stored anywhere.
Each time a customer wants to use a coupon code which has a user quota, there is a dynamic query made to the database to check the number of orders made by that user with this coupon code and it will refuse the coupon code if that number reached the quota.

The solution would be to create each time a fake order for that user with the coupon code in it. You should be able to do that with the latest version of HikaShop via the backend. You could also create a script to add that fake order manually.